1. Field of the Invention
The present invention relates to a resin-molded package, and more particularly to a resin-molded package including a resin substrate and a resin-cap defining a cavity structure and having a reduced lead inductance for an ultra-high frequency semiconductor device.
2. Description of the Related Art
It has been known that a ceramic package with a cavity structure is suitable for packaging an ultra-high frequency semiconductor device because the ceramic package reduces a dielectric constant and a parasitic capacitance of the semiconductor device. The ceramic package is disadvantageous in its high cost and expensive.
On the other hand, a resin-molded package with a cavity structure has been attracted due to its lower cost and inexpensive. The resin-molded package includes a resin substrate, on which a semiconductor chip is mounted, and a resin cap which defines a cavity in cooperation with the semiconductor chip, so that the semiconductor chip is accommodated in the cavity space. The resin cap is adhered to the resin substrate.
For the ultra-high frequency semiconductor device, it is preferable to reduce an inductance thereof for suppressing a high frequency loss thereof. To reduce the inductance, it is preferable to make short as many as possible the length of the leads. In this viewpoint, a lead-less type cavity structured package is preferable.
Japanese patent No. 2600689 and Japanese patent No. 3127584 disclose the lead-less type cavity structured packages. The lead-less type cavity structured package includes a resin substrate, a semiconductor chip mounted on the resin substrate, leads penetrating the resin substrate from an upper surface to a bottom level of the substrate and also being electrically coupled through metal wirings to the semiconductor chip, and a cap adhered to the resin substrate to define the cavity space which accommodates the semiconductor chip. This lead-less type cavity structured package is advantageous in less inductance of the leads than the leaded package with long leads which project outwardly from sides of the package and further which are bent downwardly outside the package.
The above lead-less type cavity structured packages disclosed in the above two Japanese patents have the following common disadvantages.
First, the above package is mounted on a circuit board through a solder bonding process which provides an electrical connection between the leads and conductive patterns of the circuit board. The solder bonding process is carried out by placing the package into a solder vessel which is filled with a flux. It is possible that a part of the flux enters into the cavity. If the resin substrate has a flat and horizontal top surface which bounds with the cap, then this flat and horizontal top surface makes it easy to allow the flux to enter into the cavity. If the flax enters into the cavity and further is made into contact with at least a part of the semiconductor chip, then this may provide a failure to the electrical characteristic and performance of the packaged semiconductor device.
It is necessary to prevent or avoid the entry of flux into the cavity. In order to prevent or avoid the entry of flux into the cavity, it is effective that the top flat and horizontal surface of the resin substrate has a high level from the bottom level of the substrate so as to ensure a sufficient height of the top flat and horizontal surface of the resin substrate from a top surface of the flux. This means that the height or thickness of the resin substrate is large. This resin substrate structure needs long leads which penetrate from the upper surface thereof to the bottom surface or level thereof. The long leads have a large inductance which makes it difficult to suppress the undesirable high frequency loss of the ultra-high frequency semiconductor device.
Second, the flat and horizontal top surface of the resin substrate is bounded with the cap. In order to create a sufficient cavity space for the semiconductor chip with the bonding wires, it is necessary that the cap has a sufficiently large height. This results in a large total thickness or height of the package.
Third, the cap is aligned to the resin substrate by using an automatic assembling machine. The flat and horizontal top surface of the resin substrate allows displacement or miss-alignment of the cap to the resin substrate. The package size is small, for example, a diameter of about 2 millimeters and a thickness of about 0.5 millimeters. The displacement or miss-alignment makes defective the external dimension of the package. The defective external dimension of the package makes it easy to disconnect the metal wirings.
In the above circumstances, the development of a novel package with a cavity structure free from the above problems is desirable.